This invention relates to helical gears of the type known as W-N (Wildhaver-Novikov) gears.
Generally, W-N gears are either of the single-flank or double flank form of tooth profile, taken in a transverse or normal reference plane. As is well known, one of two mating W-N gears of the single-flank form has teeth each formed on both sides thereof with a single convex flank while the other gear has teeth each formed on both sides thereof with a single concave flank. In the case of a pair of mating W-N gears of the double-flank form, both gears have teeth each formed on both sides thereof with a convex flank and a concave flank.
Meshing engagement of W-N gears of either form is effected between a convex and a concave flank, giving a substantial area of instantaneous meshing contact. Owing to this, they have a strength of tooth surface about two to three times as large as that of corresponding ordinary involute gears. They also excel involute gears on account of the bottom of tooth space defined by a single circular are of substantial radius and accordingly reduced concentration of bending stress. On the other hand, in contrast to involute gears, which make meshing contact at any instant along a line of substantial length extending over the whole face width of teeth, conventional forms of W-N gear, having each tooth flank formed of a single circular are or a curved line approximating a circular arc, only make localized meshing contact at most in two different positions along the line of tooth trace, one on the addendum portion of tooth surface.
This causes at the root of tooth a bending moment exhibiting peak values several times as high as those in the case of involute gears, giving a bending strength at most 1.5 times as large as that of involute gears. Thus, in some cases, particularly under very high loads, the gear life is limited largely by tooth breakage rather than by damage of tooth surface.
Further, the relatively high peak values of bending moment results in a substantial fluctuation of load on teeth as occurring with load transference between neighboring teeth and this causes more or less increase in noise and vibration, precluding any satisfactorily smooth power transmission particularly in high speed operations.
One prior art patent on W-N gears is U.S. Pat. No. 3,855,874 that shows double mesh type W-N gears that include gear teeth having profiles each including circular addendum and dedendum arcs connected by an intermediate straight line segment at the pitch line area.